1. Field of the Invention
This invention relates generally to electrochemical cells and, more specifically, this invention relates to consumable anode/aqueous alkaline electrolyte electrochemical cells which are capable of sustaining performance with lower volumetric flow rates of electrolyte.
2. Description of the Related Art
Electrochemical cells utilizing consumab le metal anodes are well known. Typically, the anode comprises a reactive metal, such as an alkali metal, in conjunction with a cathode and an aqueous alkaline electrolyte. In a preferred form, the anode is lithium, and the electrolyte comprises an aqeuous solution of lithium hydroxide.
The cell disclosed in Rowley U.S. Pat. No. 3,791,871 (Feb. 12, 1974), the disclosure of which is hereby incorporated by reference, typifies prior electrochemical cells. Briefly, the cell utilizes a reactive metal anode highly reactive with water and spaced from a cathode by an electrically insulating film formed on the anode in the presence of water. the anode and cathode are each in contact with an aqueous electrolyte during operation. In the embodiment shown in the Rowley patent, the anode is formed of an alkali metal such as sodium or lithium and, during operation of the cell, the electrolyte is formed by the electrochemical reaction of water and the anodic metal. The electrolyte is preferably an alkali metal hydroxide of the alkali metal utilized as the anode since such a hydroxide is naturally formed during operation of the cell and hence automatically regenerates the electrolyte during operation.
Due to anode sensitivity, however, there are a number of limitations to performance by the basic electrochemical cell. Performance of the cell undesirably fluctuates with changes in the electrolyte flow rates, with high power densities being realized at high pumping speeds. Preferably, high power densities should be achieved at low pumping speeds in order to reduce the power requirements for the pump.
Further, it is also desirable to have power remain constant over a broad range of flow rates so as to simplify multi-cell battery design.